Several different types of manufacturing method for multipole systems have become known. For quadrupole systems used for analytical purposes, honed round rods, which were fitted into suitably ground ceramic rings and secured there, were used initially. Later, hyperbolically ground metal rods were used, which were screwed into internally calibrated glass cages. The glass cages were manufactured on a precisely ground core (KPG method for “calibrated precision glass”) using a hot molding process. DE 27 37 903 (corresponding to U.S. Pat. No. 4,213,557) elucidates a method of manufacture which melts four long metal foils onto the hyperbolic interior surfaces of a similarly hyperbolic glass body during the hot molding phase of a KPG method, said foils serving as electrodes.
For the hexapole and octopole systems that are used as ion guides, round rods or capillaries are still used. The rods or capillaries have diameters of around 0.5 to 1.5 millimeters, usually around 0.8 millimeters; they are made from hard-drawn metal, usually stainless steel, and, in some cases, gold plated externally. They are secured by means of tack-welded tabs, which are screwed onto insulating rings with voltage supplies. This method of manufacture is not very reproducible, and the ion guides manufactured in this way are extremely sensitive to collisions and bending forces; they are also sensitive to mechanical or acoustic vibrations, which can cause them to resonate. They then often tear off at the tack-welded securing points. As supplied, the rods or capillaries are not very straight, and they have to be repeatedly restraightened, including after every processing operation.
Such ion guides are generally quite finely worked: the internal diameters of the rod system are usually only between two and four millimeters. Nevertheless, even slight bending, which leads to irregular internal diameters, can considerably reduce the ion transmission, or even block it completely. There is therefore a need for more stable multipole systems and for an inexpensive method of manufacture and inexpensive to manufacture.